1. Field of the Invention
The present invention relates to automatic slack adjusters of the force or clearance sensing type and more particularly to force sensing, automatic, single acting (i.e. operates automatically in the slack take-up direction only) slack adjusters of the type utilizing a torque or force limited coil slip clutch to limit adjustment torque applied to a rotatable adjustment member wherein the force limiting automatic adjustment mechanism may be selectively disengaged from the rotatable adjustment member for purposes of manual adjustment.
2. Brief Description of the Prior Art
Automatic slack adjusters for railway brakes and automative brakes of both the disc and drum type are well known. In particular, single acting automatic vehicle slack adjusters of the force sensing type (also called the clearance sensing type) wherein the adjustment mechanism will sense the forces in the brake system and either disengage the adjustment mechanism or slip when forces exceed a predetermined level, usually corresponding to the expected forces in the system when the drums or discs are contacted by the movable friction elements, to prevent over adjustment are well known and may be appreciated in greater detail by reference to U.S. Pat. Nos. Re. 26,965 and 3,507,369, both of which are hereby incorporated by reference. Clearance sensing slack adjusters wherein a torque limited friction clutch of the coil slip clutch type is utilized to limit torque applied to an adjustment member are also known as may be seen by reference to U.S. Pat. Nos. 3,507,369 and 3,901,357, both of which are hereby incorporated by reference.
While the automatic clearance sensing slack adjusters of the prior art have been generally well received, certain of the prior art devices were not totally satisfactory as the torque limited coil slip clutches were utilized in the high torque transfer direction of rotation to rotate the adjustment member in the slack takeup direction and were thus subject to be extremely sensitive to variations in friction and lubrication making manufacture and maintenance of such automatic slack adjusters more difficult and more expensive.
The automatic clearance sensing slack adjusters of the prior art were also not totally satisfactory as it was difficult or impossible to disconnect or bypass the coil clutch mechanism for manual adjustment of the brakes, such as when new friction linings were to be installed, and thus the manual adjustment operation required overpowering of the coil clutch which often resulted in operator fatigue and/or undue wear on the coil clutch mechanism.